"burn the spy!!!" [hey! 
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Dont think theres ever been a definitive answer for your question but i personally havent noticed any difference in drop rates regardless of team size. Obviously solo you'll get more drops but in a team i dont really notice.
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Positron told us, when I9 came out, what were the droprates for recipes and invention salvages (see here and here).
It's obvious that, while in team, this rate is divided by the number of people in the team, just like the XP or inf.
But, it's also known that for XP¨and inf, there is a "Team Size Multiplier" (see here), that increases the XP and inf gain for team with more members.
So, the question: does it work the same for droprates? Is the droprate multiplied by this "Team Size Bonus" while in team?